Page 335 - Carrahers_Polymer_Chemistry,_Eighth_Edition

298 Carraher’s Polymer Chemistry

tissue and can be inserted under the skin or in contact with bodily fluids generally without harm.

In the body, chitin is slowly hydrolyzed by lysozyme and absorbed. Chitin and chitosan can be
safely ingested by us and often we eat some since mushrooms, crabs, shrimp, many breads, and
beer contain some chitin. Chitin and chitosan are believed to accelerate wound healing. Chitosan is
also reported to exhibit bactericidal and fungicidal properties. Chitosan solutions are reported to be
effective against topical fungal infections such as athlete’s foot.
A continuing problem related to the introduction of bioengineering materials into our bodies is
their incompatibility with blood. Many materials cause blood to clot (thrombosis) on the surfaces of
the introduced material. Heparin (9.24) is an anticoagulant, nontoxic material that prevents clot for-
mation when coated on vascular implants. While chitosan is a hemostatic material (stops bleeding
by enhancing clotting), chitosan sulfate has the same anticoagulant behavior as heparin.

O −
O −
S O O
O
O S
O − O O O O O −
H O H O H O H O
H H
R OH H OH H OH H H H H
O H O H O H O OH H R (9.24)
H O H HN H HN
O O O H OH
S S S
O O − O O − O O −
Representative structure of heparin

Cardiovascular disease is the second—to cancer—the leading cause of death in the United
States. A contribution factor to cardiovascular disease is serum cholesterol. When ingested, chito-
san exhibits hypocholesterolemic activity. Chitosan dissolves in the low pH found in the stomach
and reprecipitates in the more alkaline intestinal fluid entrapping cholic acid as an ionic salt, pre-

venting its absorption by the liver. The cholic acid is then digested by bacteria in the large intestine.
Chitosan may also act to increase the ratio of high-density lipoprotein to total cholesterol. Chitosan
has been studied in the formation of films, including membrane-gels that immobilize enzymes and

other materials because of the mild conditions under which they form. Chitosan has been used as
a flocculate in wastewater treatment. The presence of the amine gives coacervation with negatively

charged materials such as negatively charged proteins allowing removal of unwanted protein waste.
The amine groups also capture metal ions, in particular polyvalent and heavy metal ions, such as
iron, lead, mercury, and uranium. Carraher, Francis, and Louda have also used chitosan to chelate
with platinum salts to form materials with structures similar to the anticancer drug cis-dichlrodi-
amineplatinum II chloride. The amine and hydroxyl groups can be modified through use of a wide

range of reactions, including formation of amides and esters.

Thus, there exists sufficient reason to consider these abundant materials in dietary, biomedical,
cosmetic, and so forth applications.

9.7.3 OTHERS
Mannans are found in plants, particularly some seeds, and in some microorganisms such as algae
and yeasts. Xylans are an important component of “hemicellulose,” the base soluble materials
closely associated with cellulose that are present in the secondary cell walls of higher plants. They
are generally composed of β 1→4 linked d-xylopyranose units, thus the name. Arabinans are also
plant material being present as a component of cell walls. Most arabinose-containing polysaccha-
rides are actually combinations containing various saccharide units though there are some that
contain largely only arabinose units.

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